package com.dlut.java;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.*;

public class Test2 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        if (n == 1){
            System.out.println(1);
            return;
        }
        int[] arrs = new int[n+1];
        arrs[1] = 1;
        arrs[2] = 3;
        for (int i = 3; i <= n; i++) {
            arrs[i] = i + 1 + arrs[i-2];
        }
        System.out.println(arrs[n]);
        LinkedList<Object> objects = new LinkedList<>();

    }


    class MyClass implements Comparable<MyClass>{
        Date date;
        String s;

        public MyClass(Date date, String s) {
            this.date = date;
            this.s = s;
        }

        @Override
        public int compareTo(MyClass o) {
            MyClass m = (MyClass) o;
            if (this.date.compareTo(m.date) != 0 ){
                return this.date.compareTo(m.date);
            }else
                return this.s.compareTo(m.s);
        }
    }
}
